Rhytididae (Eupulmonata) in Madagascar: reality or conjecture?

摘要

In 1990, Emberton hypothesized that the Madagascan land snail Helix covani Smith, 1879 was a previously unrecognized member of the Gondwanan family Rhytididae. The evidence put forward was based solely on features of the shell. The present paper sets out to explore this hypothesis in more detail, using morphological characters of the soft parts and molecular data, and so to test whether the present-day distribution of the Rhytididae includes Madagascar, a biogeographically interesting question. The results obtained from several independent suites of morphological characters are clearly inconsistent with the placement of Helix covani in the Rhytididae. Instead, the morphological evidence strongly supports its referral to the Acavidae, with affinity to the genus Ampelita, in which it has traditionally been classified. Molecular data are fully consistent with this, providing strong support for an acavid clade comprising Acavus, Ampelita, Helicophanta and Helix covani. Currently, the morphological and molecular data available are not sufficiently representative of Madagascan acavid diversity to permit further resolution of the affinities of the taxon in relation to Ampelita and Helicophanta.